Field of the Invention
The invention relates to an optoelectronic sensor module, in particular for use in magnetic read/write heads in magnetic recording and/or reproducing devices.
The growing complexity of available computer programs and the constantly increasing quantities of data to be stored make it necessary to develop storage media with greater and greater storage capacity. As an example, one possibility for increasing the storage capacity of a floppy-disk of the prior art (which is based on a magnetic storage technique) would be placing tracks on which information on the magnetic storage medium of the floppy disc is stored, in such a way that the tracks are closer together.
In currently available floppy-disk drives with mechanical control of a magnetic read/write head, the tracks on the storage medium are separated by approximately 100 .mu.m. A significant reduction of that separation, e.g. by a factor of 100 (which would lead to a 100-fold increase in the storage capacity of the magnetic storage medium) is not possible using magneto-mechanical tracking of the prior art. However, suitably precise tracking is possible opto-mechanically and has been used successfully for a number of years in compact disk (CD) drives. In that technique a laser beam is focussed onto the relevant disk surface and reflected back therefrom onto a suitable detector. In accordance with a pattern of lines or points on the disk which appropriately modifies the reflecting behavior of the disk, a modulated electrical signal is produced at the detector and can be used not only for data transfer but also for track recognition and tracking. That technique enables track separations in the .mu.m range to be realized.
Semiconductor components for use in optical read/write heads of optical recording and reproduction devices are known, for example, from European Patent Application 0 199 565 A3. Each of the components described therein involves integration in a silicon wafer of two photodetectors, namely a signal detector for receiving optical signals reflected from a CD and a monitor detector for monitoring a power output of an associated semiconductor laser chip.
The two photodetectors are disposed one behind the other as seen in the radiating direction of the semiconductor laser chip and lie on a beam axis of a laser beam emitted by the semiconductor laser chip. A semitransparent routing mirror disposed above the signal detector allows a small part of the radiation emitted by the semiconductor laser chip through to the monitor detector and deflects a larger part of the laser radiation away from the silicon wafer by reflecting it through 90.degree.. The reflected laser radiation reaches the CD, is reflected back to the semiconductor laser component according to the reflection pattern on the CD, passes through the semitransparent routing mirror and strikes the signal detector disposed beneath it.
However, that configuration has two disadvantages. Firstly, a laser radiation coming from the semiconductor chip and scattered by the semitransparent routing mirror strikes the signal detector directly and interferes with the optical signal reflected from the optical data storage medium. Secondly, the fabrication of semitransparent mirrors with characteristics adequate for that application is very difficult.
A known proposal exists for combining an opto-magnetic tracking with a magnetic read/write head of a magnetic storage device. That proposal includes fixing next to each other on the mechanically moved carrier arm of the read/write head, the laser source as a discrete component in the form of a semiconductor laser chip in a metallic TO packing (diameter approximately 5 mm), and the necessary beam shape and beam control optics and the associated detectors, which are also mounted in discrete metallic TO packings. However, that layout of the laser source with the associated detectors and the optical components on the carrier arm of the magnetic read/write head leads to a significant increase in both the size and the mass of the carrier arm. That results in two decisive disadvantages:
Firstly, the mobility of the arm is limited as a result of its greater inert mass and the subsequently higher acceleration forces necessary for moving it, resulting in a longer access time to the data tracks of the magnetic storage medium and therefore in a longer data access time.
Secondly, the TO components of the semiconductor laser chip and the detectors increase the dimensions of the total layout to such an extent that the standard case height of 1 inch can no longer be achieved. An opto-magnetic floppy-disk drive constructed according to that technique can therefore not directly replace magnetic floppy-disc drives of the prior art since it cannot be installed in the standard drive bay of a personal computer, let alone that of a laptop computer.
An optical sensor module is known, for example, from U.S. Pat. No. 4,958,245. That device serves for determining the position of a carrier head in relation to a magnetic data carrier and has an infrared light emitting diode, a collection lens, a routing mirror and a photodetector as separate components, which are disposed in a separate housing. The space requirement and the mass of that sensor module are also relatively large.